The present invention relates to a novel protein which has been identified in human blood and has been isolated therefrom. It is also present in the blood of other mammals, for example of the rat and of the rabbit. This novel protein appears to inhibit specifically plasminogen activator activities, namely those of tissue type plasminogen activator (t-PA) and urokinase. The protein has been called PA-binding protein (PA-BP).
It was known that plasma shows inhibition of t-PA which, for example, can be assayed with a PA-inhibition test (Thromb. Haemostas. 48, 266-269, (1982)). It was assumed that this inhibition was due to a well-characterized PA inhibitor (In: Recent Advances in Blood Coagulation, L. Poller, ed; Churchill Livingstone NY, Vol. 4, pages 11-33, (1985)) which had been found also in blood platelets, endothelium cell media and liver cell media.